Three different groups of animals—insects, birds, and mammals—include species that have evolved the ability to fly. This ability developed independently in each group through separate evolutionary processes. Recent research has shown that a fourth group of animals, the now-extinct winged reptiles known as Pterosaurs, were probably capable of true flight as well. Whereas the aerodynamics of flight apply equally to all types of flying animals, the mechanical details of flight vary significantly among the groups.

All insects, birds, and mammals that fly move themselves forward by flapping their wings. They do not depend exclusively on gliding and soaring to remain aloft. However, many species of birds combine extensive gliding and soaring with episodes of true flight to conserve energy.

Forward flight is produced in all true flying animals in a similar way. Each animal moves its wings up and down in a circle or figure-eight pattern...